Generic electro-optical measuring devices, in particular handheld laser distance measuring devices, such as described, for example, in WO 2005/083465, for the optical measurement of distances have been known for years and are currently used in large numbers for the most variant applications, particularly in the construction industry. They can be used for the optical measurement of distances, for example between a measurement stop of the measuring device and a surface region of an object within a distance measurement range from a few decimeters up to, for example, 30 meters with an accuracy of a few millimeters. In this case, in a conventional embodiment of such a measuring device, optical beams modulated via an optics are emitted as transmitted beams or measuring light beams to the object to be measured. At least a portion of the measuring light beams is retroreflected from the surface region of the object in the direction of the measuring device. Beams reflected from the surface region (particularly, in a fashion spaced apart from the transmitted beams) are collected again via the optics and converted into an electric signal by a receiver of the device.
Such known electro-optical measuring devices and distance measurement devices are based on a measurement of the propagation time of a temporal light pulse, or a measurement of the phase shift of a laser beam reflected from the object.
During measurement of the propagation time, the pulse propagation time from the laser light source to the object and back from the laser to a receiver is measured. An advantage of this embodiment is the extremely short measuring time required. Disadvantageous is the correspondingly required very high time resolution of the light pulse detection in the nanosecond or even picosecond range, something which makes high demands on the detection technology, in order to measure distances with a resolution in the centimeter or even millimeter range.
Electro-optical measuring devices and distance measurement methods based on measurement of the phase of the reflected laser light are based on the fact that the phase shift in the reflected laser beam, or the modulation thereof in comparison with the emitted beam is a function of distance. Typically, a frequency modulation of the laser light amplitude is carried out, and the phase angle of the signals modulated thereon is evaluated.
An advantage of this second variant of the measurement method is a higher achievable resolution of the distance measurement in comparison with the propagation time method in conjunction with a comparable outlay on metrology.
A disadvantage of this second variant is based on a lack of uniqueness in the measurement in the case of distances and/or resulting phase shifts of a multiple of half the laser or modulation wavelength. This ambiguity can be canceled by taking measurements at different laser wavelengths and/or modulation frequencies, but this increases the measuring time. This solution is widely used in commercially available laser distance measuring devices.
Known electro-optical distance measuring devices, in particular handheld laser distance measuring devices, have in common that the resolution of the measurement of the distance relating to a targeted point in space is typically served by a key on the measuring device that is to be actuated by a user, or served by a field to be marked by touching on a touchscreen as the display of the device.
Given such an operation for triggering the measurement by a mechanical command input, unintended adjustment of the measuring device from an originally provided targeting direction can easily come about, with the consequence that the alignment of the laser beam is significantly shifted away from a previously targeted point in space as a function of distance, for example of the order of magnitude of several centimeters, the result being inaccurate measurement results, in particular in the case of measurements over long distances.
A known alternative is remote triggers, for example cable remote triggers or infrared/Bluetooth remote triggers (compare the mechanical wire release known for over a century in the field of photography), with the aid of which it is possible to trigger a measurement without needing to touch the device directly at all. However, it is disadvantageous in this case and complicated (with regard both to operability and to technical and/or design features) that this requires a separate remote triggering device connected to the actual measuring device (mechanically and/or electronically), and this always also needs to be carried along and operated by the user during a measurement task.